INTERACTIVE EFFECTS OF ELEVATED CO2 AND O-3 ON RICE AND FLACCA TOMATO

Atmospheric concentrations of both carbon dioxide (CO2) and ozone (O-3 ) are increasing, with potentially dramatic effects on plants. This st udy was conducted to determine interactive effects of CO2 and O-3 on r ice (Oryza sativa L. cv. IR 74) and a 'wilty' mutant of tomato (Lycope rsicon esculentum Mill. flacca). Plants were grown from seed in a glas shouse and exposed for 28 days to ambient or elevated CO2 (approximate to 400 or 700 mu l l(-1) CO2) and/or ambient or elevated O-3 (peak/va lley pattern of exposure with cumulative totals of approximate to 1 or 44 mu l l(-1) h). Elevated CO2 alleviated O-3-associated decreases in allocation of biomass to roots, as indicated by a decreased root:shoo t ratio (p < 0.05), and also reduced injury from O-3 as indicated by l eaf greenness readings for one experiment(p < 0.05). By itself, elevat ed CO2 resulted in increases in total plant and individual organ(root, leaf, stem) dry weights and root:shoot ratio and elevated O-3 resulte d in increases in main culm leaf number and a decrease in stem dry wei ght (p < 0.05). Elevated CO2 had no significant effect on the tendency for O-3-induced biomass reductions of flacca tomato. For flacca, elev ated CO2 alone increased shoot and root biomass (p < 0.05), and elevat ed O-3 alone tended to decrease biomass for both parameters, but only at p = 0.09 and O.11, respectively. This study was preliminary, as the environmental conditions in these experiments may have altered O-3 an d CO2 responses of the plants. However, these results provided additio nal evidence that elevated CO2 inhibits adverse effects of O-3 on plan ts, and that the interactive response may be mediated by stomata. (C) 1997 Elsevier Science B.V.